This invention relates to zinc sulfide-based electroluminescent phosphors. More specifically, it relates to zinc sulfide-based electroluminescent phosphors co-activated with manganese and copper.
Current commercial white-emitting electroluminescent (EL) phosphors are made by blending green-emitting, blue-emitting, and orange-yellow-emitting EL phosphors in appropriate ratios. The major disadvantages of this blending method are that (1) the color emitted by the EL lamp is not homogeneous upon being closely examined because the particles of the three phosphor components emit different colors; (2) the emitted color of the lamp shifts with time because the brightness decay curves of the three phosphors are different; and (3) depending on the particular brightness of each component, the blending ratio may have to be adjusted several times in order to obtain desired color. Therefore, it would be an advantage to have a single-component white-emitting EL phosphor.
It is an object of the invention to obviate the disadvantages of the prior art.
It is another object of the invention to provide a single-component white-emitting electroluminescent phosphor.
It is a further object of the invention to provide a zinc sulfide-based electroluminescent phosphor having a white emission when stimulated in a thick-film electroluminescent lamp.
It is yet another object of the invention to provide a method for making a single-component white-emitting electroluminescent phosphor.
In accordance with one object the invention, there is provided a single-component white-emitting electroluminescent phosphor having an emission having an x color coordinate of 0.23 to 0.41 and a y color coordinate of 0.25 to 0.42.
In accordance with another object of the invention, the single-component white-emitting electroluminescent phosphor comprises zinc sulfide activated with copper, manganese, chlorine, and, optionally, one or more metals selected from gold and antimony.
In accordance with still another object of the invention, there is provided a method for making a single-component white-emitting electroluminescent phosphor comprising:
(a) forming a first mixture by combining amounts of zinc sulfide, a source of copper, zinc oxide, sulfur, a chloride-containing flux, and, optionally, a source of one or more metals selected from gold and antimony;
(b) firing the first mixture in air at a temperature from about 1100xc2x0 C. to about 1250xc2x0 C. for about 3 to about 5 hours to form a first-fired material;
(c) washing the first-fired material to remove the flux;
(d) mulling the first-fired material to induce defects in the crystal structure;
(e) washing the first-fired material to further remove flux residues and copper sulfides;
(f) forming a second mixture by combining the first-fired material with amounts of a copper source, a manganese source, and zinc oxide;
(g) firing the second mixture in air at a temperature from about 700xc2x0 C. to about 950xc2x0 C. for about 2 to about 5 hours to form a second-fired material; and
(h) washing the second-fired material to remove chemical residues to form the phosphor.